Analysis And Evaluation Of Nitrogen Flow In The Food Chain System

Nitrogen, one of the important components of protein, is also an important nutrient for plant growing and animals. Nitrogen management quality is directly related to the "population-resources-environment-food security" and other major issues. Long term's high nitrogen input in agriculture production system cause lower nutrient efficiency and serious environment problem. Therefore, it is necessary to analyses nitrogen flow in food chain system, evaluate the reasonableness of nitrogen flow. Based on method of Material Flow Analysis (MFA), we adopted nitrogen flow model in the food chain in China (CNFC) to analyse the status of nitrogen flow in different regions (Beijing Municipality, Tianjin Municipality, Hebei Province, Henan Province, and Shandong Province) of the Huang–Huai–Hai. Considering the relationship of resources, environment, efficiency, and other factors, The indicators of nitrogen flow in food chain were selected to built evaluation framework of nitrogen flow in food chain system; Combining the results of model calculations as well as the Analytic Hierarchy Process (AHP), the quantitative evaluation of nitrogen flow in food chain was obtained in different regions of the Huang– Huai– Hai. The results showed that:1. There was a great nitrogen flux in Huang–Huai–Hai region and nitrogen flow was tower-type distribution in food chain system, which was the highest nitrogen flux in agriculture production system, household consumption system least, and livestock production system in the middle. And nitrogen surplus in agriculture production system was very high, and the highest surplus achieves 32.04 M t. by the year of 2003. Synthesis nitrogen was the major input in agriculture production system and synthesis nitrogen input reached 75.19 M t in 2007, but grain nitrogen yield was 44.91 M t only. However, nitrogen emission into the environment was significantly higher than that of farmland surplus. Close to grain N yield, nitrogen emission into the environment was totally 42.63 M t. And nitrogen flow in livestock production system, the self-sufficiency rate of feed nitrogen showed a downward trend year by year, but feed nitrogen import increases yearly. Local feed grain nitrogen became main feed nitrogen input now. And in household consumption system, fauna and flora food nitrogen could meet self-sufficiency completely; and at the same time, there was a lot of food nitrogen exported, in which fauna food nitrogen showed an increasing trend year by year, but flora food nitrogen had a decreasing trend. And Fauna and flora food nitrogen exported 6.41, 2.82 M t in Huang–Huai–Hai Region in 2007. So, nitrogen flow in food chain in Huang-Huai-Hai region was high input, low production output, high environment emission system, and net imports in feed nitrogen and net export in fauna and flora food nitrogen.2. Rationality indices (S) in five regions of Huang–Huai–Hai had shown decline in varying degrees over the years, of which rationality indices were all less than 0.7 and different regions had different changes. Compared with 1988, rationality indices decreased by 0.34, 0.37, 0.15, 0.27 and 0.38 respectively in 2007. And because of their level of economic development and different agricultural production levels, nitrogen flow rationality indices in different sub-systems in different regions had difference with the year change, of which rationality indices in agricultural production systems (S1), household consumption systems (S3) and system betweens (S4) were all on the decline over the time, but livestock production systems (S2) was all reasonable increasing in different regions.3. Analyzing external factors of impact of rationality indices of N flow in food chain can be seen: there were very significant negative correlations between rationality indices of nitrogen flow in food chain (S) and level of urbanization, economic development and per capita income respectively.4. Analysis of main nitrogen flow indicators change in different systems to the impact of rationality index sensitivity in food chain can be seen: different systems in different regions had different impact of S. From a whole, it had been found that efficiency indicator, environmental indicator and waste recycling indicator of household consumption system had the highest effect on the S, followed by livestock production systems, and agricultural production system was the smallest. Compared different indicators, it had been found that waste recycling indicators changes in different sub-systems had high effects on S, environmental indicator the second and efficiency indicators the third. If enhancing efficiency indicator 5 percentages and environmental indicator 5 percentages in sub-systems at the same time (indicated by△S), it could been found that household consumption system had the highest effect on S. Instead of efficiency indicator and environmental indicator in agricultural production system and livestock production system, which all had less effects on S. Therefore, focus on different indicators of different systems, taking different measures to optimize systems or indicators sensitive to S was an important way to enhance rationality indices of nitrogen flow in food chain system.